Ribozyme speed limits

Mechanism of RNA cleavage under mildly acidic conditions. In the range of approximately pH 3 to 5, specific acid and base produce β (purple), γ (red), and δ (green) catalysis. β Catalysis by specific acid changes the nature of the reaction pathway by allowing 5 to exist as an intermediate long enough to allow pseudorotation to 6. This in turn allows departure of the 3′ oxygen to form a 2′,5′-phosphodiester linkage, 7. Other notations as in the legend of Figure 4.